Integrated circuits, especially those with surfaces that are exposed to human contact, are susceptible to damage resulting from electrostatic discharge (ESD), short circuits, mechanical damage, and similar occurrences. These occurrences can induce latch-up conditions in at least a portion of the integrated circuit or can produce other damage that results in excessive or over currents. These over currents can cause the integrated circuit to get too hot, rupture junctions, short circuit across insulators, open circuit conductors, malfunction, and even melt. The increased temperature can injure a user, can generate current overloads that damage the power supply or battery of the integrated circuit, of companion circuits, or any combination of these.
Some prior art solutions use protection switches. The protection switches are placed external to the integrated circuit so that they will not be exposed to the ESD events or other occurrences, thus protecting them from damage suffered by other portions of the integrated circuit. These protection switches contain a current detection circuit, a current switch, and a reset signal generator. When latch-up occurs, the current detection circuit detects excessive current consumption and disconnects the entire integrated circuit from the power supply source for a time sufficient to remove the latch-up conditions. When the power supply voltage is restored, the reset circuit returns the digital blocks that form the integrated circuit to their initial conditions. The reset circuit also sets a flag to indicate to a host processor that the data previously stored in the digital blocks is lost or is unreliable.
These external protection switches increase the cost of the final product of which they form a part. They also take up space on printed circuit boards. Space is typically at a premium on small, portable products such as cell phones and personal digital assistants. These external protection switches also reset the entire integrated circuit every time latch-up occurs, even when only a small portion of the integrated circuit is affected by latch-up. This occurs even though some areas of the integrated circuit are often not affected by latch-up, are undamaged, and consequently do not need to be reset.